Since the fever is associated with chills he will need to be examined and undergo investigations such as CBC, Dengue IgM, Lepto IgM, WIDAL, etc to find the underlying cause of the problem and have it treated accordingly. Make sure he's well hydrated and gets the supportive medicines to control the situation.
Next Steps
Follow the steps as advised
Health Tips
If condition persists or worsens visit the ER at the earliest